🎯 PHP Expectations – Validate Assumptions with assert() and Runtime Checks

Learn how to use expectations in PHP to enforce assumptions and catch errors early during development using the assert() function and exception-based validation.

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🧲 Introduction – What Are Expectations in PHP?

Expectations in PHP refer to runtime conditions that your program expects to be true during execution. The assert() function allows developers to define assertions—conditions that must hold true. If an assertion fails, PHP can raise a warning or throw an exception (depending on the configuration).

Expectations are especially useful in development, unit testing, and debugging, helping you identify logic errors early.

🎯 In this guide, you’ll learn:

• How to use assert() in PHP
• Configure PHP to throw exceptions on failed assertions
• Common use cases for expectations
• Best practices for error detection

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🎯 PHP Expectations with assert()

assert(condition, description);

• Condition: An expression expected to be true
• Description: Optional error message if the condition is false

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✅ Basic Example

$age = 25;
assert($age > 0, "Age must be positive");

📌 If $age is less than or equal to 0, this triggers a failure

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⚙️ Configure assert() Behavior

PHP allows control over assertion behavior through INI directives:

ini_set('assert.active', 1);               // Enable assertions
ini_set('zend.assertions', 1);             // Keep code active (default: 1 in dev, -1 in prod)
ini_set('assert.exception', 1);            // Throw AssertionError instead of warning

✅ This makes assertion failures behave like exceptions:

try {
    assert(false, "Something went wrong");
} catch (AssertionError $e) {
    echo "❌ Assertion failed: " . $e->getMessage();
}

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🧪 Use Cases for Assertions

Scenario	Example
Type validation	assert(is_int($id))
Range checks	assert($score >= 0 && $score <= 100)
Logic assumptions	assert($start < $end)
Dependency presence	assert(class_exists('UserController'))
Testing dev-only logic	assert(!empty($mockData))

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🛡️ Best Practices

• ✅ Use assertions in development only, not for production logic
• ✅ Use assert.exception = 1 for exception-based handling
• ✅ Keep assertions separate from application flow (not for user input errors)
• ❌ Do not use assertions as a replacement for input validation or access control

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🔍 Alternative to assert() – Manual Expectations

Sometimes you want to enforce strict runtime conditions with custom logic:

if (!$user) {
    throw new Exception("User not found");
}

📌 This is preferred for critical failures or user-facing logic

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📌 Summary – Recap & Next Steps

PHP expectations using assert() provide a lightweight mechanism to enforce assumptions, catch bugs early, and document intent during development. When configured properly, assertions can throw exceptions and integrate into your debugging or testing workflow.

🔍 Key Takeaways:

• Use assert() to define conditions your code expects to be true
• Enable exceptions using assert.exception = 1 for better error handling
• Use assertions during development, not for production error management
• Prefer exceptions for user input or flow control

⚙️ Real-World Use Cases:
Unit testing, precondition checks, development debugging, internal API validation

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❓ Frequently Asked Questions (FAQs)

❓ Is assert() enabled by default?
⚠️ In production (zend.assertions = -1), assertions are ignored. You must enable it explicitly in dev.

❓ Can I catch assertion failures like exceptions?
✅ Yes. Set assert.exception = 1 and use try { ... } catch (AssertionError $e) {}.

❓ Should I use assert() for validating user input?
❌ No. Use proper input validation and error handling for that.

❓ Can I disable assertions entirely in production?
✅ Yes. Set zend.assertions = -1 and assert.active = 0 in php.ini.

❓ Are assertions logged automatically?
❌ Not by default. Use a logging library inside catch blocks or via custom handlers.

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